Method of making electrically heated fabric structures



March 22, 1966 R. -A. SMITH ETAL METHOD OF MAKING ELECTRICALLY HEATEDFABRIC STRUCTURES Original Filed Sept. 22. 1961 United States PatentThis is a division of United States patent application Serial No.140,082, filed September 22, 1961.

The present invention relates to the manufacture of electrically heatedfabric structures, such as blankets, pads,

rugs, drapes, clothing and the like.

In the manufacture of conventional electrically heated fabricstructures, as for example blankets, a grid of electrical conductors isdisposed within a preformed fabric shell or envelope which is thenclosed, as by stitching. While efficient, conventional electric blanketshave not met with wide acceptance, primarily because of appearance andhigh cost. Generally, the presence of the grid of electrical conductorsis apparent on the blanket surface as a series of ribs, and provides fora relatively heavy or bulky construction. The high cost of such blanketscan be attributed to the relatively expensive fabric from which theblanket shell is formed and to the cumbersome and time consuming task ofinserting the electrical conductors within the shell itself.Accordingly, a primary object of this invention is to provide a new orgenerally improved and more satisfactory method for making electricallyheated fabric structures.

A further object is the provision of a method for making electricallyheated articles wherein an unbroken film or web of thermoplasticmaterial is printed with a desired electric conducting circuit, and thenneedle-punched to project fibers from opposite sides thereof.

These and other objects and advantages of the present invention areobtained by applying, preferably by printing, an electric circuit ontoan unbroken web or film followed by needle-punching a batt or web ofunwoven fibers onto, the printed film to project fibers from oppositesides thereof.

The electric circuit may be printed onto a surface of the unbroken filmby conventional procedures and is so arranged as to provide for uniformheating along substantially all portions of the resulting fabric ordifferential heating along selected areas thereof, depending upon itsintended end use. In designing the electric circuit to satisfyparticular heat requirements, the length or path of the circuit shouldbe such as to minimize the cross-sectional size of the electricconductor, especially when the finished fabric is intended for use inapplication where fabric flexibility and drape are importantconsiderations.

The needle-punching apparatus which is suitable for use in the practiceof the present invention is of conventional construction, and includes aseries of barbed needles which perforate the film, including those filmareas which are printed with electric conducting materials, andconcomitantly punch or drive the fibers of the batt partially throughsuch perforations. As the needles are projected through the film, andparticularly the uncoated portions thereof, the perforations or openingswhich are formed each include an irregular or jagged edge surface whichtend to bite into or grip the fibers which have been driven into andextend through the film. During the withdrawal of the barbed needlesfrom the film, the biting or gripping effect exerted on the punchedfibers by the jagged edge surfaces of the film perforations discouragefiber movement so that the fibers project approximately to the same icedegree from opposite sides of the film base in the finished product. Inmost applications, however, it is preferred that a batt of fibers beapplied to and punched through opposite sides of the film based tosecure maximum coverage for decorative or insulating purposes.

The gripping action exerted by the jagged edge openings of the film baseadapt the needle-punched fabric, and articles made therefrom, forvarious uses without any further treatment. However, where repeated and/or rugged use of the resulting needle-punched fabric or article iscontemplated, it is preferred that the punched fibers be more securelyanchored to the film base. This may be effected by integrally bondingthe projecting fibers in a base film of thermoplastic character bycausing a controlled flow of the film material around and intoengagement with the punched fibers. Such flow of the film material maybe achieved by heating the same to within the softening range of thethermoplastic material from which the fil-rn is formed, anddesirably,.subjecting either the film or the needle-punched fabric topressure so as to encourage the flow of the film material as it assumesa softened condition. Upon setting or cooling of the softened film, theportions of the punched fibers enveloped by the thermoplastic basematerial are firmly embedded. Aside from the standpoint of economy andease of manufacture, this heat-treating procedure has no detrimentaleffects on the printed electric circuit, the punched fibers or the filmbase, and avoids an undesired stiff or hard feel from being introducedinto the fabric.

Heating of the thermoplastic base film of the needlepunched fabric maybe achieved by merely passing the same through a hot gaseous atmosphere,as provided for example by a series of resistance heating elements orinfrared lamps. This procedure assures retention of the soft and fiuffycharacter of the punched fibers but generally requires a relatively longheating zone to obtain a desired flow of the thermoplastic base'material around the punched fibers. An alternative method is to impingeat least one side of the needle-punched fabric with a heated fluid whichis under sufficient pressure to encourage flow of the thermoplasticmaterial of the base film as it is softened. Such fluid may simplyconsist of a hot gas or a mixture of a heated liquid and gas, such assteam. Ho-t air alone performs the desired function and is extremelypractical since it may be continuously reheated and recirculated andinvolves no removal or recovery problems. The temperature and pressureof the heated fluid employed will, of course, depend upon the softeningtemperature range of the particular thermoplastic material from whichthe film base is formed aswell as the character and coverage provided bythe fibers punched into the film base. Generally, the punched fiberswill offer some thermal insulation and thus may require that theimpinging heated fluid be at a temperature Well within or even slightlyabove the softening temperature range of the base film.

As a still further alternative, activation of the film base may beachieved by engaging the needle-punched fabric between a pair of heatedmetal pressure plates of endless belts. With this procedure theneedle-punched fabric is compressed while the film base is heated towithin its softening temperature range so that the finished fabricpresents pile surfaces which are of greater density or coverage than theinitial needle-punched fabric. The temperature and pressure of theheated plates or belts will depend upon the same consideration as setforth above, in addition to the degree of fiber densification d si Fromthe description of the invention given above it will be apparent thatthe film base of the needle-punched fabric must be of non-fibrous, soft,and non-brittle or pliable character so as to facilitate the formationof irregular or jagged edge openings or perforations as the barbedneedles are projected therethrough without initiating tearing of thefilm. In effect, the films employed in the fabric of the presentinvention readily yield to forces applied by the barbed needles withouttransmitting or distributing such forces to any substantial area of thefilm. A variety of thermoplastic materials are presently available forproviding films having the essential properties for satisfactorilypracticing the invention described. Examples of such thermoplastic filmsinclude films formed of vinyl resins, such as polystyrene, polyvinylchloride, polyvinyl chloride acetate, polyvinylidene chloride,polytetrafluoroethylene, and polyvinyl butyral, and polymeric resins,such as nylon, and including polyolefin resins, such as polyethylene andpolypropylene.

Aside from the essential characteristics of the film base noted above,the particular film employed will, of course, depend upon the propertiesdesired in the finished fabric and, as more fully described thereafter,the nature of the covering fibers. In applications where theelectrically heated fabric will not normally be subjected to substantialtensions or stretching forces which might cause rupture of the printedcircuit, a base film which is in an unoriented condition issatisfactory. Alternatively, such base film may be unilaterally orientedto provide a fabric which is yieldable along one restricted direction,or biaxially oriented to provide the finished fabric with substantiallyfixed dimensions. The thickness of the film base may be varied tosatisfy strength requirements and/ or drape characteristics desired inthe finished fabric. Further, from the decorative standpoint, the filmmay be transparent, translucent, opaque, or pigmented. When makingfabrics having a sparse fabric covering or pile along one surface only,as for example for use as electrically heated floor mats or rugs, thefilm may be embossed with a pattern or may be roughened to impartdecorative and/ or skid resistant properties to the fabric.

The fibers driven or punched into the film base may be natural fibers orsynthetic fibers or various combinations of different natural and/orsynthetic fibers. Suitable natural fibers include fibers such as cotton,linen, wool and silk. The synthetic fibers may be formed ofthermoplastic materials, as for example from vinyl and polymeric resinsheretofore noted, cellulosic fibers, such as rayon, and mineral fibers,as for example spun glass. Aside from providing fibers which offergreater resistance to electric flow than the material forming theprinted electric circuit, no particular restrictions exists as to theselection of fibers for use in needle-punched fabrics in which frictionalone is to be relied upon for holding the fibers in place. When it isdesired to have the fibers embedded within the film base by the heattreating procedure described above, care must be exercised in selectingfibers which possess the required stability at the elevated temperaturesencountered during softening of the film base. Stability as employedherein pertains not only to the material from which the fiber itself isformed, but also to any finishes, pigments, dyes or other additivesapplied to or incorporated within the fibers.

The properties of the fibers employed may, of course, be varied tosecure desired end results. For example the surfaces of the fibers maybe roughened or otherwise treated to enhance their frictional contactwith the film base, they may be pigmented or dyed and may have moistureabsorbent or repellent characteristics. Further, fibers of differenttypes or colors may be punched into the film base in accordance with apredetermined pattern, or the stroke of the barbed needles of theneedlepunching apparatus may be suitably adjusted to provide a pilesurface in which the degree of fiber projection varies along differentareas of the fabric.

From the above description of the invention, it will be apparent thatthe needle-punching operation has no effect on the continuity of thatportion of the film base or printed circuit which extends between thepunched fibers. With needle-punched fabrics which have been subjected tothe heat treatment described, the continuity and strength of the fabricbase are both greatly improved by the elimination of areas at whichtearing may initiate and the provisions of strong bonds between punchedfibers and base. The continuous and unbroken film structure of thefabric base which extends between the punched fibers performs the samefunctions as that of a woven or knitted base of a conventionalneedle-punched fabric. More important, this film structure can serve asa means for modifying or supplementing the properties imparted to thefinished fabric by the fibers themselves. For example, a fabric formedby punching moisture absorbent fibers into a base film having lowmoisture absorption and transmission characteristics, would be soft yetstrong, with the film base serving as a moisture barrier while thepunched fibers facilitating air passage without substantial moisturetransmission. The ability of such fabric to breathe or transmit airrenders the same highly suitable for use in a variety of articles suchas floor coverings, pads, bedding articles including mattress covers,blankets, etc., while the combined air transmission and moistureabsorption characteristics makes such fabrics ideal for use in garments.

As a further alternative, both the fibers and base film of theneedle-punched fabric may be formed of materials having low moistureabsorption and transmission characteristics. A fabric of this naturewould possess moisture barrier characteristics yet would exhibit thedesired feel and appearance of a pile textile fabric. Such fabric may beutilized in applications where canvas is now employed and would beespecially useful in the manufacture of winter garmets and foot wear.

In the accompanying drawings, illustrative of the invention:

FIGURE 1 is a diagrammatic view generally illustrating one mode ofpracticing the method of the present invention;

FIGURE 2 is a vertical section through a portion of the fabric base asit is subjected to the needle-punching operation;

FIGURE 3 is a bottom view of a portion of the fabric base shown inFIGURE 2;

FIGURE 4 is a side view of an apparatus for use in heat treating aneedle-punched fabric of the present invention while maintaining thesame under pressure;

FIGURE 5 is a side view of the non-woven fabric as made by the processin FIGURE 1; and

FIGURE 6 is a view similar to that shown in FIGURE 5 showing aneedle-punched fabric after being heat treated by the apparatus inFIGURE 4.

In practicing the method of the present invention with the apparatus ofFIGURE 1, a combed or carded web of fibers 15 is advanced from a sourceof supply over guide roll 17 and into a nip formed by rollers 19 and 21where it is engaged with a continuous, unbroken, non-fibrous film 23formed of thermoplastic material. As illustrated, the film 23 isprovided with a series of independent printed electric circuits 25 whichare applied to at least one surface thereof. The circuits 25 are formedby conventional procedures and include a thin, planar, mass or layer ofelectric conductive materials bonded to the film along a predeterminedpattern or path for satisfying particular heat requirements. Preferably,at least the printed portion and, if desired, the entire printed surfaceof the film 23 may be coated or covered with a continuous film ofmaterial which is the same or similar to that from which the film 23 isformed, and more particularly a material which softens at a temperatureat least equal to the softening temperature of the film 23. For the sakeof simplicity and ease of description, the electric circuits 25 areillustrated as being laid along a serpentine or sinuous path with theirends terminating adjacent to each other along the same longitudinal edgeof the film 23. Such L" d) circuit arrangement may be suitable, forexample, in an electric blanket construction. It will be understood,however, that the materials employed in forming the electric circuitsand the dimensions and arrangement or path of such circuits can bevaried to satisfy the particular heat characteristics desired in thefinished article.

From the rollers 19, the printed film 23 and superposed film web ispassed through and into a needle-punching loom, indicated generally at26, having a series of reciprocable barbed needles 27 which drive orpunch the fibers of the web 15 through the film 23, including theprinted portions thereof. Upon completion of the needle-punchingoperation, the resulting fabric may be collected for use, oralternatively, may be passed through a heat-treating chamber 29 wherethe film base 23 is softened by a heated fluid, as circulated byconduits 31, to anchor the punched fibers as more fully describedhereinafter.

The needle-punching loom 26 operates in the conventional manner whereinthe series of barbed needles 27 are reciprocated toward and through film23 to drive the fibers of the web 15 therethrough, and then outwardlyfrom the film 23 to permit the latter to be advanced relative to theloom itself. During the fiber-punching stroke of the loom 26, the barbedneedles 27 puncture or perforate the film 23 and concomitantly drive thefibers of the web 15 partially therethrough. As best seen in FIGURES .2and. 3, the perforations or openings 33 formed in the film 23 as thebarbed needles 27 are forced therethrough .each exhibit irregular orjagged edge surfaces 35 which bite into the fibers projected through thefilm and snugly grip the same. As the series of barbed needles 27 aremoved through their return stroke to withdraw the same from the film 23,this biting or snug gripping of the punched fibers by the jagged edgesurfaces 35 of the film perforations 33 prevents the punched fibers frommoving along with the barbed needles. The punched fibers are thereforelocked in their projected positions and, as a result, with the method ofthe present invention the production of needle-punched fabrics havinggenerally similar pile surfaces on its opposite sides may be readilyachieved.

While the fibers of the needle-punched fabric formed by theabove-described method may be pulled out from the film, there issufficient locking of the fibers, however, so that the fabric is adaptedfor various applications without any further treatment. Where ruggedand/ or repeated usage of the fabric is contemplated, the punched fibersmay be more securely anchored to the film base 23. This fiber anchoragemay be achieved by the use of adhesive compounds as employed inconventional needlepunched fabrics. To avoid the numerous disadvantageswhich are incorporated into the fabric by such adhesive compounds, thepreferred procedure, in accordance with the present invention, is tosoften the material from which film 23 is formed and cause the same tofiow around and into contact with the projected fibers. Once theprojected fibers are embraced by the material of the film 23, the filmis set so that the fibers and films form an integral structure.

Softening of the film 23 may, of course, be achieved by suitablesolvents. However, in view of problems involved in solvent removal orrecovery, a preferred procedure is to subject the needle-punched fabricto a heat treatment designed to elevate the temperature of thethermoplastic film 23 to within its softening range but below itsmelting range. This heat treatment may be achieved as shown in FIGURE 1wherein the needlepunched fabric is passed through a chamber 29 withinwhich a heated fluid, preferably hot air, is impinged against onesurface of the fabric. The impinging hot air may be withdrawn from thechamber 29, reheated, and continuously recirculated through the conduits31 and thus provides for an economical, simple and clean procedure. Thetemperature of the impinging hot air must be such as to render the filmsoft without actually melting the same and will depend upon suchconsiderations as the character of the thermoplastic film 23, thecoating applied to the printed circuit, and the punched fibers, thethermal insulating effect or coverage offered by the punched fibers, theperiod of treatment, etc. As heretofore mentioned, care must beexercised to select fibers which are stable under the elevatedtemperature conditions required for softening of the film 23. Thepressure of the impinging hot air should be such as to encourage theflow of the softened material of the film 23 into embracing relationshipabout the punched fibers, yet avoid damage to the film or printedcircuit.

The needle-punched fabric issuing from the chamber 29 after beingsubjected to the heat treatment described generally retains the soft andfluffy character of the original needle punched fabric. The punchedfibers are bonded to the film 23 in the areas in which the openings 33were first formed, with the portions of the film 23 extending betweenthe projecting fibers still retaining an unbroken film structure. Theabove-described fabric possesses a soft and pleasant feel and exhibitsgood drape characteristics.

With the modified procedure as illustrated in FIGURE 4, however, theoriginal needle-punched fabric may be converted into a fabric havingmore body, simultaneously as the fibers are anchored or embedded withinthe film 23. The apparatus for practicing this modified heat-treatingprocedure includes a pair of endless metal belts 37 which are trainedover rollers 39 and 41 and driven by suitable means, not shown. Asillustrated, the opposing reaches of the belts 37 pass over idler rolls43 which cooperate with the adjacent rollers 39 to form a graduallyconverging entrance portion 45. Heating means 47 are positioned alongthe paths of the opposing reaches of the endless belts 37 formaintaining the same at a desired elevated temperature.

In operation, the original needle-punched fabric is passed into theentrance portion 45 and between the op posing reaches of the endlessbelts 37 which are prefer ably adjusted to exert a pressing action onthe fabric as it is carried through the apparatus. The opposing reachesof the belts 37 are kept at a desired elevated temperature by theheating means 47 so as to achieve a softening of the thermoplasticmaterial forming the film 23, and a flow of the softened material intoembracing relationship about the punched fibers. The conditions ofoperation for this modified procedure will, in general, depend upon thesame considerations as noted with regard to the heattreating methodillustrated in FIGURE 1, in addition to the degree of fiber compactiondesired. As diagrammatically illustrated in FIGURE 6, the fabric treatedin accordance with this modified procedure possesses rather dense orcompact pile surfaces as a result of the combined heating and pressingaction of the endless; belts 37. The degree of fiber compaction may, ofcourse, be varied as desired by adjusting the spacing between theopposing reaches of the belts 37.

To provide for a uniform heating and pressing of the needle-punchedfabric, the belts 37 are preferably in the form of endless sheets havingcontinuous or unbroken surfaces. It will of course be apparent that thebelts 37 may be in the form of endless screens of fine mesh, in whichcase the heating means 47 may supply hot air. Alternatively, the belts37 may be formed with projecting portions or openings so that theneedle-punched fabric may be embossed with a desired pattern during theheattreating stage.

The resulting needle-punched fabric, with or without being subjected tothe heat treatment described above, is then severed between theindependent elctric circuits 25, as indicated by the broken lines 49, toprovide a series of individual units. An electric supply cord,preferably including a step-down transformer, is then connected to theends of the printed circuit in a conventional manner to Complete themanufacture of the electrically heated structure which may be, forexample, an electric blanket. Since only a single film is employed, thefinished article is light in weight and of less bulk than correspondingconventional structures. Further, a thin layer of electricallyconductive materials required for providing a desired heating circuitdoes not detract from the appearance of the finished article nor addsubstantial weight thereto.

While the method of making the electrically heated structure has beendescribed as involving the needlepunching of only one web of cardedfibers onto the film 23, it will of course be apparent that such fiberwebs may be needled onto opposite surfaces of the film 23 Withoutdeparting from the spirit and scope of the invention.

It is to be understood that changes and variations may be made withoutdeparting from the spirit and scope of the invention as defined in theappended claims.

We claim:

1. A method of making an electrically heated fabric structure includingthe steps of depositing a thin layer of electrically conductive materialalong a predetermined path on at least one surface of an unbroken,non-fibrous, thermoplastic, polymeric film and adhering the samethereto, disposing a batt of fibers onto said film, and projecting thefibers of said batt into and partially through said film, including theportions thereof onto which the electrically conducting material hasbeen deposited and adhered.

2. A method as described in claim 1 wherein said electrically conductivematerial is printed onto said film and wherein said fibers are projectedthrough said film by a plurality of barbed needles which form openingsin said film having jagged edge surfaces for gripping the fibersprojected therethrough.

3. A method of making an electrically heated fabric structure includingthe steps of depositing a thin layer of electrically conductive materialalong a predetermined path on at least one surface of an unbroken,non-fibrous, thermoplastic, polymeric film and adhering the samethereto, disposing a batt of fibers onto said film, needle-punching thebatt of fibers onto said film including the portions thereof onto whichthe electrically conducted material has been deposited and adhered,effecting a controlled flow of the film material around and intoengagement with the needle-punched fibers, and setting the film materialto anchor said fibers to said film.

4. A method as defined in claim 3 wherein said controlled flow of filmmaterial is effected by heating the same to within its softeningtemperature range.

5. A method of making an electrically heated fabric structure includingthe steps of printing a thin layer of electrically conductive materialalong a continuous path onto at least one side of a non-fibrous,thermoplastic, polymeric film and projecting fibers into the filmthrough the printed and unprinted portions thereof, the portions of thefilm extending between said fibers remaining in continuous and unbrokenconstruction.

References Cited by the Examiner UNITED STATES PATENTS 2,619,580 11/1952Pontiere 219-528 2,724,674 11/ 1955 Pritkin.

2,745,942 5/1956 Cohen 219528 2,951,278 9/1960 Hoffman 151154XR2,955,351 10/ 1960 McCreadie.

3,010,180 11/1961 Hoffman 161154XR FOREIGN PATENTS 607,656 9/1948 GreatBritain.

EARL M. BERGERT, Primary Examiner.

3. A METHOD OF MAKING AN ELECTRICALLY HEATED FABRIC STRUCTURE INCLUDINGTHE STEPS OF DEPOSITING A THIN LAYER OF ELECTRICALLY CONDUCTIVE MATERIALALONG A PREDETERMINED PATH ON AT LEAST ONE SURFACE OF AN UNBROKEN,NON-FIBROUS, THERMOPLASTIC, POLYMERIC FILM AND ADHERING THE SAMETHERETO, DISPOSING A BATT OF FIBERS ONTO SAID FILM, NEEDLE-PUNCHING THEBATT OF FIBERS ONTO SAID FILM INCLUDING THE PORTIONS THEREOF ONTO WHICHTHE ELECTRICALLY CONDUCTED MATERIAL HAS